Copying material for use in high-speed electrophotography

ABSTRACT

A HIGH-SPEED ELECTROPHOTOGRAPHIC COPYING MATERIAL COMPRISING A SUPPORT AND A PHOTOCONDUCTIVE LAYER FORMED OF A BINDER AND COATED ON ONE SURFACE OF SAID SUPPORT, IN WHICH THE BLINDER COMPRISES A MIXTURE CONSISTING OF (I) A COPOLYMER PRODUCED BY POLYMERIZING ONE OR MORE POLYMERIC MONOMERS CONTAINING NITROGEN AND ONE OR MORE VINYL MONOMERS TOGETHER AND (II) ONE OF THE FOLLOWING; COPOLYMER (1), MIXTURE (2), AND MIXTURE (3): (1) A COPOLYMER OF (B) HYDROXYETHY-(OR METHA) ACRYLATE AND (BI1) VINYL MONOMER HAVING CARBOXYLIC ACID RADICALS. (2) A MIXTURE OF (C) A COPOLYMER FORMED FROM THE ABOVE-MENTIONED CARBOXYLIC ACID MONOMER AND (C-1) THE AFOREMENTIONED VINYL MONOMER, AND AN ORGANIC ACID ANHYDRIDE, (3) A MIXTURE CONSISTING OF THE COPOLYMER AS DESCRIBED IN (1) AND THE ORGANIC ACID ANHYDRIDE MENTIONED IN (2).

y 1971 AKIYOSHI msumom ETAL 3,5

COPYING MATERIAL FOR USE IN HIGH-SPEED ELECTROPHOTOGHAPHY Filed Oct. 23, 1968 mmwzmooma mwvp wk) ACID COMPONENT CONTENT /100 ZINC OXIDE) United States Patent O US. Cl. 961.5 ll Claim ABSTRACT OF THE DISCLOSURE A high-speed electrophotographic copying material comprising a support and a photoconductive layer formed of a binder and coated on one surface of said support, in which the binder comprises a mixture consisting of (I) a copolymer produced by polymerizing one or more polymeric monomers containing nitrogen and one or more vinyl monomers together and (II) one of the following; copolymer 1), mixture (2), and mixture (3):

( 1) a copolymer of (b) hydroxyethyl-(or metha) acrylate and (b-l) vinyl monomer having carboxylic acid radicals.

(2) a mixture of (c) a copolymer formed from the above-mentioned carboxylic acid monomer and (c-l) the aforementioned vinyl monomer, and an organic acid anhydride,

(3) a mixture consisting of the copolymer as described in (1) and the organic acid anhydride mentioned in BACKGROUND OF THE INVENTION (a) Field of the invention The present invention is concerned with a copying material for use in high-speed electrophotography comprising a support and a photoconductive layer formed on one surface of said support by a binder comprising a copolymer containing nitrogen.

(b) Description of the prior art In the electrophotographic copying materials of the prior art, it was the practice to use a metallic plate or a paper sheet processed to have an electric conductivity as a support, upon whose surface is coated a layer of resin binder containing dispersed therein a photoconductive substance and light-sensitive substance or sensitizer. In preparing the binder for such copying materials, various kinds of resins such as silicone resin, alkyd resin, styrene-butadiene resin, and vinyl resin were conventionally used. The binder to be used in manufacturing electrophotographic copying materials is required not only to bind the photoconductive substance and the light-sensitive substance to the support but also to improve the electrostatic chargeability of the photoconductive layer when the layer is impressed with an electric charge to have electrostatic photosensitivity, not to decrease the sensitivity of the photoconductive layer whose particulars will be referred to later, and to enhance the weather-proofness of the copying materials. None of the abovementioned resins conventionally used were satisfactory enough to enable the binder to meet all of these necessary physical requirements, and especially in those countries where both temperature and relative humidity are high, there has been a strong demand for the development of copying materials which have an excellent weather-proofness. Furthermore, as mentioned later, a copolymer containing nitrogen, or a copolymer comprising a polymeric monomer containing nitrogen,

which is one of the components of the binder used in the present invention, generally has a low specific resistance and poor insulation resistance. Accordingly the electrophotographic copying materials, whose photoconductive layer is formed of such a binder, exhibit a remarkable decrease of charge potential while left standing in the dark after having been impressed with an electric charge, which inevitably leads to the necessity of having the copying materials processed on the copying machine, which is capable of exposing and developing, in a very short time immediately after same have been impressed with an electric charge. Otherwise the copying materials were too unsatisfactory to be used for practical purposes. Moreover, even when such copying as this is possible, the image thus produced on the electrophotographic copying materials of the prior art was an extremely blurred one.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide highly sensitive electrophotographic copying materials which are substantially superior in copying properties to the conventional copying materials and specially adapted for use in a high-speed copying machine, by preparing a binder made with a copolymer containing nitrogen as a basic component and another specific copolymer, mixed together to make such nitrogenous copolymer applicable as a binder.

More particularly, this invention relates to the manufacture of high-speed electrophotographic copying materials having an extremely high sensitivity and weatherability, in which a binder comprising a mixture of (I) a copolymeric compound comprising a copolymer having a polymeric monomer which contains nitrogen, as a basic component in an amount not exceeding 40 mole percent and (11) another specific copolymer, is used to form a light-sensitive layer on the surface of the support.

The copolymer (I) containing nitrogen to be used for making the binder which is employed in the present invention is prepared from (a-l) at least one member of polymeric monomer containing nitrogen, the monomer amount not exceeding 40 mole percent, chosen from the group consisting of (a1-a) nitrogen-containing unsaturated compounds (A) as defined hereinbelow, and

alkylammoniurn salts of unsaturated compounds (B) as defined hereinbelow such as the trimethyl ammonium salt, triethylammonium salt, tripropyl ammonium salt, and the aromatic ammonium salts of unsaturated compounds (B) such as the benzyl ammonium salt. The respective unsaturated compounds (A) and (B) have the respective chemical structures (A) and (B) mentioned below:

(A) Unsaturated compounds structure where R represents a radical selected from the group consisting of H, --CH CgHq, C H halogen and alkylhalide (C -C radicals,

X represents a radical selected from the group consisting of CN, CONR and CONHCH O'R' (where R represents a radical selected from the group consising of H, -CH C H -C H phenyl radical and benzyl radical) (B) Unsaturated compound structure I? GHQ 0 C O OH where R" represents a radical selected from the group consisting of -H and -CH;,. The nitrogen-containing monomer is copolymerized with (a) at least one member of acrylic esters or methacrylic esters such as methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, butylacrylate, and butylmethacrylate, and polymeric vinyl monomers such as styrene, butadiene, vinyl acetate and vinyl chloride are mixed together and copolymerized by the ordinary method. In the present invention, a binder made with a mixture of the aforementioned polymeric monomer containing nitrogen (hereinafter referred to as N-polymer), whose amount in the mixture does not eX- ceed an amount of 50% by weight, and one of the following (1) copolymer, or (2) mixture, or (3) mixture is used.

(1) Copolymer.A copolymer (hereinafter referred to as HC-polymer) obtained by polymerizing either (b) hydroxyethylacrylate or hydroxylethylmethacrylate and (b-l) as least one of vinyl monomers having carboxylic acid radicals such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, together with (b-2) at least one of the vnyl monomers (inluding the aforementioned esters) used in the above mentioned N-polymer.

(2) Mixture.A mixture consisting of a copolymer (hereinafter referred to as A-polymer) polymerised from (c) at least one of the aforementioned carboxylic acid monomers and (c-l) at least one of the vinyl monomers (including esters) mixed together with at least one member selected from the group consisting of phthalic acid anhydride and maleic acid anhydride.

(3) Mixture.A mixture of the aforementioned H-C- polymer and the abovementioned organic acid anhydride.

It is the object of the present invention to improve the weather-proofness of the photoconductive layer by making the aforementioned copolymer contain carboxylic acid monomers as a component thereof or by adding acid anhydrides to the copolymer. There is, however, the drawback that the electrosatic sensitivity of the photoconductive layer decreases as the amount of the aforementioned acid components increases. In this invention, due consideration is given to this problem so that the photoconductive layer of the copying materials will keep a wholly satisfactory sensitivity and weather-proofness by mixing up to 50% by weight of N-polymer with copolymers which contain the the aforementioned acid components or polymers to which such acid components are added (HC- polymer and A-polymer).

It is to be noted also that the copying materials referred to in the present invention are made with the aforementioned binder, to which photoconductive substances such as zinc oxide and light-sensitive substances or sensitizers such as Bromophenol Blue, fluorescein, Rose Bengal, etc. are added, then dispersed in a proper solvent to make a solution to be used for making a photoconductive layer. The solution is applied onto the upper surface of a support which is either a metal plate or a paper sheet whose under surface is treated with an electroconductive substance, and finished by drying.

The electrophotographic copying materials prepared according to this invention as described in the foregoing exhibit an excellent electrostatic chargeability, less dark decay, lower fatigue of the light-sensitive components after the prior exposure to the light in the process of copying, and much improved weather-proofness, thus satisfying all the properties required of the aforementioned copying materials.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a graph of curves showing the effect of the content of the acid component, which is contained in or added to the binder prepared according to the present invention, on the sensitivity of the photoconductive layer and the weather-proofness.

The term acid component, as used herein, comprehends carboxylic acid contained in HC-polymer, carboxylic acid contained in A-polyrner and organic acid anhydride contained in HC polymer. The acid component content on the axis of abscissa in the graph presents the whole quantity expressed by millimole of the aforementioned acid component contained in the gross volume of the binder, which is used in making the photoconductive layer, per 100 g. of zinc oxide contained in the photoconductive layer of the copying materials.

The explanation of the graph showing the relation of acid component content vs. sensitivity and weather-proofness will be made in the following. In the graph, the curve 1 shows the change of the sensitivity of the copying materials when the acid component contained in the binder of the photo-conductive layer is increased. The scale shows the time (unit: second) required for the electric potential to drop by half when the photo-conductive layer is exposed to the light. The conditions under which the curve was obtained will be described in detail in Example l. The curve 2 in the graph shows the change of the weather-proofness of the copying material when the acid component contained in the binder of the photoconductive layer is increased. Weather-proofness is indicated by the value obtained by dividing dark decay (saturated potential V potential at the time of the exposure to the light V by the saturated potential. It will be observed in the graph that when the acid component contained in the binder is increased, the sensitivity increases, while the weather-proofness decreases markedly.

According to the present invention, in case an organic acid anhydride is added in said binder, it is desirable to add the organic acid anhydride in amount not exceeding 2 millimoles per 100 gr. zinc oxide, and in case a HC- polymer or an A-polymer is contained in said binder, it is desrable for the acid component to be contained in amount not exceeding 5 parts by weight per 100 parts by weight of HC-polymer or A-polymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further illustrated in detail in the following examples.

EXAMPLE 1 (1) Preparation of N-polymer A copolymer of the binder was prepared by polymerizing according to the known method parts by weight of styrene, 10 parts by weight of butylacrylate, 15 parts by Weight of acrylonitrile, and 5 parts by weight of acrylamide by the use of xyrene and butanol for polymerization solvent.

(2) Preparation of HC-polymer A copolymer of the binder was prepared by polymerizing according to the known method 50 parts by weight of styrene, 40 parts by weight of ethyl acrylate, 15 parts by weight of fi-hydroxyethylmethacrylate, and 3 parts by weight of acrylic acid by the use of xylene, toluene, and butanol for polymerization solvent.

Then the following photoconductive substances-dispersed solutions (a), (b), and (c) were prepared by the use of the respective copolymers made according to the items (1) and (2) mentioned above.

() Zinc oxide for electrophotography use: 100 g.

H-C polymer: 20 g. Sensitizer-same as in (a): 1 cc. Toluene: 150 cc.

Then the solution (a) was applied onto the surface of a paper sheet whose reverse side had been processed to have an electroconductivity and then dried to obtain an electrophotographic copying material. The respective solutions (b) and (0) were also applied onto the front surfaces of the support sheets processed to have an electroconductivity as mentioned above and were dried to obtain electrophotographic copying materials with the purpose of making a comparison of their merits and performances.

The efficiency tests were made for the respective copying materials thus prepared by measuring their electrostatic characterstics as mentioned below:

V electric potential on the copying materials when impressed with an electrostatic charge for 30 seconds by corona discharge of --6 kv. after the copying materials had been kept in a normal atmosphere (at a temperature of 20 C. and a relative humidity of 65%) and in an atmosphere of a high temperature and a high relative humidity (at a temperature of 30 C. and a relative humidity of 80-85%) respectively (saturated potential).

V electric potential on the copying materials when the materials are left standing in the darkness for 30 seconds after having been impressed with an electric charge (dark decay: V -V /2ztime required for the electric potential to decrease by half when exposed to the light of 6 luxes at the time of the electric potential standing at V mentioned above (sensitivity) V -electric potential on the copying materials when impressed with an electric charge as mentioned in the above by being exposed to the light of 500 luxes for one minute (prior exposure) before the electric charge was impressed in the case of V V /V -dark decay property (the larger the value, the better the property).

V' /V degree of fatigue of the prior exposure (the larger the value, the better the property).

The results of the efficiency measurements are shown in the following table:

to the present invention produced a satisfactorily clear copied image free from such defects as seen on specimens (b) and (c) and proved that they were ideal copying materials to be used on a high-speed copying machine. Incidentally, the copying materials prepared with the aforementioned photoconductive substance-dispersed solution (a), when trail mixed with 0.1 gr. of phthalic acid anhydride, sowed a t /2 value approximately similar to that of the solution (a) and a V /V value of 0.80.

EXAMPLE 2 (1) Preparation of N-polymer A copolymer of the binder was prepared by polymerizing according to known method 75 parts by weight of styrene, 10 parts by weight of butylacrylate, 5 parts by weight of N-methylol acrylamide, and 10 parts by weight of acrylonitrile by the use of xylene and butanol for polymerization solvent.

(2) Preparation of H-C-polymer A copolymer of the binder was prepared by polymerizing according to the ordinary method 55 parts by weight of styrene, 30 parts by weight of butylacrylate, 10 parts by weight of B-hydroxyethylmethacrylate, and 4 parts by weight of maleic anhydride by the use of toluene an butanol for polymerization solvent.

Then the following photoconductive substance-dispersed solutions (a), (b) and (c) were prepared by the use of respective copolymers made according to the item (1) and (2) mentioned above.

TABLE 1 Kept at auormal temperature and RH. Kept at a high temperature and RH. Copying material V.. (V) Vo/Vs t (see.) V's/Va VB (V) Vo/Va t% (sec) V's/Vs (a) Copying material of this invention 500 0. 85 3. 0 0.75 400 0.70 2. 0 0. 62 (b) Specimen for comparison. 100 0. 1O 0. 40 0. 40 (c) Specimen for comparisom- 500 0. 85 6. 5 0. 75 400 0.70 4. 0 0.

NOTE .-The negative sign in the above table shows that the value obtained was too small to be measured.

The electrophotographic copying material was prepared by the use of the solution (a) with the same processes described in Example 1. The solutions (b) and (c) were also processed similarly to prepare the electrophotographic copying materials for comparing merits and efficiency of the respective copying materials thus prepared. Table 2 shows the results of the measurements obtained from the respective copying materials operated for copy ing in the same testing procedures taken in Example 1.

TABLE 2 Kept at a normal temperature and RH. Kept at a high temperature and RH.

Copying material Vs (V) Vu/Vi (sec) /m s o/ a a e (a) Copying material of this invention 550 0. 85 3. 0 0. 500 0. 65 3. 0 0. 65 (b) Specimen for comparison 150 0. 27 1. 0 0. 43 5O O. 40 (c) Specimen for comparison" 600 0. 85 6. 0 0. 450 0. 70 40 0. 60

When the copying materials of the present invention were tried for copying, a very clearly copied image was obtained on them, and it was also proved that they were ideal copying materials to be used on a high-speed copying machine.

EXAMPLE 3 (1) Preparation of N-polymer A polymer was prepared by polymerizing after the ordinary method 70 parts by weight of methyl methacrylate, 15 parts by weight of butyl acrylate, parts by weight of acrylonitrile, and 5 parts by weight of acrylic acid by the use of toluene and butanol for polymerization solvent, to which an equivalent weight of trimethylamine was added to make carboxylic acid quaternary, thus providing the copolymer required for the binder.

(2) Preparation of A-polymer A copolymer of the binder was prepared by polymerizing after the ordinary polymerization method 65 parts by weight of styrene, 40 parts by weight of butylacrylate, and 2 parts by weight of methacrylic acid by the use of xerene for polymerization solvent.

Then the following photoconductive substance-dispersed solutions (a), (b), and (0) were prepared by the use of acid anhydride and the respective copolymers which had been made according to the abovementioned items (1) and (2).

The solution (a) was applied onto the surface of the metallic plates of aluminum, dried, and electrophotographic copying materials were accordingly obtained. The respective solutions (b) and (0) were also applied on the surface of the metallic plates of aluminum, dried, and

electrophotographic copying materials were also prepared for the comparison of efficiency of the respective copying materials. The efficiency tests were made for the respective copying materials by the same measurements and procedures taken in the case of Example 1, the results of which are shown in Table 3.

TABLE 3 copying machine, they produced a very clearly copied image. The excellent properties of the copying materials of this invention proved that they were ideal copying materials for a high-speed electrophotographic copying machine.

EXAMPLE 4 (1) Preparation of N-polymer A copolymer of the binder was prepared by polymerizating after the ordinary method 7-0 parts by weight of styrene, '20 parts by weight of butylacrylate, and 10 parts by weight of acrylonitrile by the use of toluene for 1 polymerization solvent.

(2) Preparation of HC-polymer A copolymer of the binder was prepared by polymerizing after the ordinary method parts by weight of vinyl acetate, 20 parts by weight of methyl methacrylate, 15 parts by weight of butylacrylate, 12 parts by weight of B-hydroxyethyl-methacrylate, and 3 parts by weight of acrylic acid by the use of toluene and ethyl acetate for polymerization solvent.

The following photoconductive substance-dispersed solutions (a), (b), (c), and (d) were then prepared by the use of the respective copolymers which were made according to the preparation described in the items (1) and (2) in the foregoing.

The electrophotographic copying materials were obtained first by the application of the solutions (a) and (b) onto the surface of the support paper, whose reverse side had been processed to have an electroconductivity, and then by drying the applied solution. While other types of electrophotographic copying materials were also prepared by applying the solutions (c) and ((1) respectively onto the surface of the support paper whose reverse side had been primarily processed as mentioned in the foregoing and dried to make specimens for comparison. obtained are shown in Table 4.

The copying materials thus prepared were then meas- Kept at a normal temperature and RH. Kept at a high temperature and Eli.

Copying material Vs (V) Vo/Vg t% (see) Va/VB V! (V) V /V. fl (see) V.,/V

(2.) Copying material of this invention 450 0. 85 3. 0 0. 70 400 0. 78 2. 5 0. (b) Specimen for comparison. 150 0. 45 0. 50 80 0.70 (c) Specimen for comparison. 400 0. 85 5. 0 0. 380 0. 79 4. 0 0. 50

When the copying materials which had been prepared ured of their electrostatic characteristics in a manner according to the present invention were tried on the similar to that described in Example 1 and the results TABLE 4 Kept at a normal temperature and RH. Kept at a high temperature and R.H.

Copying material Vs (V) Vo/Vs t fi (sec.) V. (V) VOIV. tk (see) V's/V (a) Copying material of this invention 500 0. 85 3. 450 0. 75 2. 0. 65 (b) Copying material of this invention.. 450 0. 92 2. 9 430 0. 83 2. 5 0. 58 (c) Specimen for comparison 150 0.30 50 0.70 (d) Specimen or comparison 500 0. 85 4. 5 450 0. 75 4. 0 0. 60

The copying material (a) prepared according to the present invention was subjected to copying operation on the copying machine and a very clear copied image was obtained. Another copying material (b) of this invention proved itself of being able to be a copying material having an excellent weather-proofness even under the atmospheric conditions of high temperature and high relative humidity in case an acid anhydride was put in the solution for forming photoconductive layer in addition to H-Opolymer.

What is claimed is:

1. In an electrophotographic copying material comprising an electroconductive support having on one surface thereof a photoconductive layer comprising photoconductive zinc oxide particles dispersed in a resinous hinder, the improvement wherein said binder consists essentially of a mixture of (I) a nitrogen-containing copolymer, as defined below, and (II) a second component selected from the group consisting of 1) an HC copolymer, as defined below, (2) an A copolymenas defined below, mixed with an organic acid anhydride selected from the group consisting of phthalic acid anhydride and maleic acid anhydride, and (3) said H-C copolymer mixed with an organic acid anhydride selected from the group consisting of phthalic acid anhydride and maleic acid anhydride;

said nitrogen-containing copolymer consisting of a copolymer of (a) at least one polymerizable monomer selected from the group consisting of methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, butyl acrylate, butylmethacrylate, styrene, butadiene, vinyl acetate and vinyl chloride,

(a-l) at least one polymerizable nitrogen-containing monomer selected from the group consisting of (a-l-a) monomers of the formula wherein R is selected from the group consisting of H, -OH3, C2H5, C3H7, 11310- gen and alkylhalide in which the alkyl contains from 1 to 3 carbon atoms, and

X is selected from the group consisting of -CN, -CON(R') and -CONHCH OR' wherein R is selected from the group consisting of -H, -OH -C H -C H phenyl and benzyl,

(a-l-b) trimethyl, triethyl, tripropyl and benzyl ammonium salts of unsaturated acids of the formula wherein R" is selected from the group consisting of -H and -CH the amount of said nitrogen-containing monomer in said nitrogen-containing copolymer being less than about 40 mole percent; said HC copolymer consisting of a copolymer of (b) a monomer selected from the group consisting of hydroxyethylacrylate and hydroxyethylmethacrylate,

(b-l) at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, maleic acid and itaconic acid,

(b-2) at least one monomer selected from the group consisting of methacrylate, methylrnethacrylate, ethylacrylate, ethylmethacrylate, butylacrylate, butyl methacrylate, styrene, butadiene, vinyl acetate ad vinyl chloride;

said A copolymer consisting of a copolymer of (c) at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, cro tonic acid, maleic acid and itaconic acid,

(c-l) at least one monomer selected from the group consisting of methacrylate, methylmethacrylate, ethylacrylate, ethylrnethacrylate, butylacrylate, butylmethacrylate, styrene, butadiene, vinyl acetate and vinyl chloride;

the amount of the nitrogen-containing copolymer (I) in said mixture being less than about by weight based on the total weight of said mixture.

References Cited UNITED STATES PATENTS 3,245,786 4/1966 Cassiers et a1. 96-1 3,159,483 12/ 1964 Bermenbur'g et al 96-1 3,174,854 3/1965 Stiirnpf et al 96-1 3,390,987 7/1968 Tomanek 96-15 3,482,970 12/ 1969 Solodar 96-15 DONALD LEVY, Primary Examiner M. B. W-ITTENBERG, Assistant Examiner US. Cl. X.R. 

